[fix][broker] Fix uncompleted future when get the topic policies of a…

… deleted topic (apache#18824)

Fix the uncompleted future when getting the topic policies of a deleted topic.
https://github.com/apache/pulsar/blob/30b52a1ac11b4be485258140a167b5e635586a36/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/SystemTopicBasedTopicPoliciesService.java#L513-L535
`future.complete(null);` when `msg.getValue() == null`.

(cherry picked from commit b311961)
(cherry picked from commit 1d98196)

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/SystemTopicBasedTopicPoliciesService.java

@@ -531,6 +531,8 @@ private void fetchTopicPoliciesAsyncAndCloseReader(SystemTopicClient.Reader<Puls
                         } else {
                             fetchTopicPoliciesAsyncAndCloseReader(reader, topicName, policies, future);
                         }
+                    } else {
+                        future.complete(null);
                     }
                 });
             } else {

pulsar-broker/src/test/java/org/apache/pulsar/broker/admin/TopicPoliciesTest.java

@@ -3077,4 +3077,22 @@ public void testProduceChangesWithEncryptionRequired() throws Exception {
                     assertNotEquals(newLac, beforeLac);
                 });
     }
+
+    @Test
+    public void testGetTopicPoliciesWhenDeleteTopicPolicy() throws Exception {
+        admin.topics().createNonPartitionedTopic(persistenceTopic);
+        admin.topicPolicies().setMaxConsumers(persistenceTopic, 5);
+
+        int maxConsumerPerTopic = pulsar
+                .getTopicPoliciesService()
+                .getTopicPoliciesBypassCacheAsync(TopicName.get(persistenceTopic)).get()
+                .getMaxConsumerPerTopic();
+
+        assertEquals(maxConsumerPerTopic, 5);
+        admin.topics().delete(persistenceTopic, true);
+        TopicPolicies topicPolicies =pulsar.getTopicPoliciesService()
+                .getTopicPoliciesBypassCacheAsync(TopicName.get(persistenceTopic)).get(5, TimeUnit.SECONDS);
+        assertNull(topicPolicies);
+    }
+
 }